In a case where a skin condition is analyzed by using an image generated by photographing the skin, it is difficult to accurately detect the shapes of sulci cutis and cristae cutis if a body hair is shown in the image. As a result, analysis precision becomes lower. In view of this, the use of an image from which body hairs have been removed has been considered, so as to increase the precision of skin condition analyses. Therefore, it is essential to accurately detect body hair regions in an image.
Meanwhile, there has been a suggested technique for separating body hair pixels constituting a body hair region in an image from background pixels constituting the regions that are not the body hair region (see Patent Document 1, for example). Specifically, by the technique disclosed in Patent Document 1, body hair pixels are detected by performing binarization to turn pixels into pixels equal to or greater than the mode of the pixel values in the image and pixels smaller than the mode, or body hair pixels are detected by extracting the contour of a body hair with a Sobel filter.